PFAC Invertebrate Sampling

 

The Anglers’ Riverfly Monitoring Initiative (ARMI) is a national scheme, launched by the Riverfly Partnership in 2007, to enable anglers and other interested groups and individuals to actively monitor and protect their local rivers.  It helps ensure rivers are monitored more widely and at a greater frequency than is possible by the Environment Agency alone.

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Anglers are natural guardians of the river environment and this initiative gives us a simple technique to monitor water quality.  It puts us in direct communication with the local Ecological Contact of the Environment Agency.  Further, it acts as a deterrent to incidental polluters.

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Riverflies, along with other freshwater invertebrates, are at the heart of the freshwater ecosystem and are a vital link in the aquatic food chain.  Riverfly populations are affected by many factors, predominately water quality, habitat diversity, water level and flow rate.  Their common characteristics of limited mobility, relatively long life-cycle, presence throughout the year and specific tolerances to changes in environmental conditions make them powerful biological indicators to monitor water quality.

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The ARMI monitoring technique involves taking 3-minute kick samples (normally broken into six 30-second sessions at differing areas at each site to try and avoid sample bias) from the river-bed each month, and recording the presence and abundance of eight pollution-sensitive invertebrate groups (caddis, various up-wing flies, stoneflies and shrimps).  If invertebrate numbers drop below a ‘trigger level’, the Environment Agency is notified so that the problem can be identified and action taken.

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Abundance in the sample is recorded at the following levels: 1-9 organisms / sample (abundance A) scores 1; 10-99 organisms / sample (abundance B) scores 2; 100-999 organisms / sample (abundance C) scores 3; ≥ 1000 organisms / sample (abundance D) scores 4.  The total number per sample is called the “Angler’s Score Index” (ASI). 

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PFAC hold nine years’ data on invertebrate sampling on the River Noe and tributaries at three sites (Fig 1: Peakshole Water and River Noe beats 2 and 7 – encompassing both the White Peak and the Dark Peak).  We can use deviations from this important baseline as evidence of a pollution incident; we can present our evidence to the Environment Agency and we can use it to monitor recovery from any deleterious event.

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The presence of true Mayfly (Ephemeridae), Blue Winged Olives (Ephemerellidae) and Stone clingers (Heptageniidae) indicates high water quality.  Regarding the Heptageniidae, March Browns appear early (Mar/Apr); Claret Duns and Olive Uprights are expected around May with Autumn Duns around August / September.  Yellow Mays are not currently found on the River Noe although we intend to take steps to reintroduce them.

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The presence of Caddis (200 species of Trichoptera) and Stoneflies (Plecoptera, Fig 12) indicates moderate / high quality water.  Caseless caddis include Rhyacophila (Sand Sedges, Apr-Oct) and Hydropsyche (Grey Flags, May-Aug and Marbled Sedges, May-Sep).  Of the cased caddis, Grannom appear Apr/May; Welshman’s Button (Jun-Aug), Cinnamon Sedge (May-Sep) and Caperers (Sep-Nov).  

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Freshwater shrimps (Gammarus) and Olives (Baetidae) are less dependent on high quality water.  Freshwater shrimps require water of moderate quality and Olives can survive in water of low / moderate quality.   Large Dark Olives peak in Mar/Apr but most Olives (Iron Blues, Medium Olives, Pale Wateries) make an appearance in May with Large Dark Olives, Iron Blues and Pale Wateries peaking again in Sep-Oct. 

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PFAC possesses a unique body of data and it is absolutely imperative that we continue our invertebrate sampling programme in order to protect our river.  Additionally, the trends in the species groups give a good guide to anglers on the fly patterns that predominate during certain periods of the year.